Although various physiological and biochemical functions have been studied in fetal and in neonatal mammals, the role of the individual components of the birth process in inducing the changes which occur after birth, have not been well delineated. In this project, it is planned to examine the role of some of the events which occur at birth on circulatory, metabolic, and hormonal adjustments. The studies will be conducted in chronically-instrumented fetal lambs, in utero, and various perinatal events will be simulated. These include the effects of: 1) pulmonary ventilation in utero, with no change in blood gases, 2) ventilation with air or oxygen to increase arterial saturation to postnatal levels, 3) umbilical cord occlusion, 4) body cooling without stimulating cutaneous receptors, 5) surface cooling, and 6) combination of ventilation, oxygenation, and cooling. The effects of these events on the following will be studied: a) general circulatory responses including heart rate, intracardiac flows and cardiac output and its distribution, b) hormonal responses, particularly of catecholamines and thyroid hormones, c) metabolism of carbohydrate and fatty acids, d) myocardial blood flow and metabolism, and g) gastrointestinal blood flow and metabolism.